Influence of vestibular and visual stimulation on split-belt walking.

We investigated the influence of vestibular (caloric ear irrigation) and visual (optokinetic) stimulation on slow and fast split-belt walking. The velocity of one belt was fixed (1.5 or 5.0-6.0 km/h) and subjects (N = 8 for vestibular and N = 6 for visual experiments) were asked to adjust the velocity of the other belt to a level at which they perceived the velocity of both the belts as equal. Throughout all experiments, subjects bimanually held on to the space-fixed handles along the treadmill, which provided haptic information on body orientation. While the optokinetic stimulus (displayed on face-mounted virtual reality goggles) had no effect on belt velocity adjustments compared to control trials, cold-water ear irrigation during slow (but not fast) walking effectively influenced belt velocity adjustments in seven of eight subjects. Only two of these subjects decreased the velocity of the ipsilateral belt, consistent with the ipsilateral turning toward the irrigated ear in the Fukuda stepping test. The other five subjects, however, increased the velocity of the ipsilateral belt. A straight-ahead sense mechanism can explain both decreased and increased velocity adjustments. Subjects decrease or increase ipsilateral belt velocity depending on whether the vestibular stimulus is interpreted as an indicator of the straight-ahead direction (decreased velocity) or as an error signal relative to the straight-ahead direction provided by the haptic input from the space-fixed handles along the treadmill (increased velocity). The missing effect during fast walking corroborates the findings by others that the influence of vestibular tone asymmetry on locomotion decreases at higher gait velocities.

Periodic-pattern-selective cells in monkey visual cortex.

To study the visual processing of periodic and aperiodic patterns, we have analyzed neuronal responses in areas V1 and V2 of the visual cortex of alert monkeys during behaviorally induced fixation of gaze. Receptive field eccentricities ranged between 0.5 degrees and 4 degrees. We found cells that responded vigorously to gratings, but weakly or not all to bars and edges. In some cells the aperiodic stimuli even reduced the activity below the spontaneous level. The distribution of a bar-grating response index indicated a discrete population of "grating cells" characterized by more than 10-fold superiority of gratings. We estimated that these cells have a frequency of 4% in V1 and 1.6% in V2, and that about 4 million grafting cells of V1 subserve the central 4 degrees of vision. The converse, cells that responded to isolated bars but not to gratings of any periodicity, was also observed. The grating cells of V1 were mostly (23 of 26) found in layers 2, 3, and 4B. They preferred spatial frequencies between 2.6 and 19 cycles/degree (median, 9.3), with tuning widths at half-amplitude between 0.4 and 1.4 octaves (median, 1.0). Their tunings were narrower, and their preferred frequencies higher, than those of other cells on average. Grating cells were also narrowly tuned for orientation. Those of V2 were similarly selective. The responses of grating cells depended critically on the number of cycles of the gratings. With square waves of optimum periodicity responses required a minimum of 2-6 grating cycles and leveled off at 4-14 (median, 7.5). The corresponding receptive field widths were 0.34-2.4 degrees (median, 0.78 degrees) for V1 and 0.72-2.4 degrees (median, 1.4 degrees) for V2. Grating cells typically gave unmodulated responses to drifting gratings, were unselective for direction of motion, and were strongly activated also by stationary gratings. Half of those of V1 were monocular, the others binocular, some showing strong binocular facilitation and disparity sensitivity. Length summation was usually monotonic, but strong end-inhibition was also observed. In contrast to other cells, grating cells were not activated by harmonic components. Spatial-frequency response curves for sine-wave, square-wave, and line gratings were similar. Square-wave gratings of one-third the preferred frequency failed to excite the cells, while the isolated 3f component (f = the fundamental of the square wave) of these gratings evoked strong responses. In spite of the nonlinear features, grating cells had low contrast thresholds.(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebrospinal fluid immunoglobulins and multiple sclerosis. Correspondence with magnetic resonance imaging and visually evoked potential changes.

The clinical (disability) and paraclinical (visually evoked potential [VEP]/magnetic resonance imaging [MRI]) data of patients with definite or probable multiple sclerosis (MS) were compared with their cerebrospinal fluid (CSF) immunoglobulins taken within the same period of time. For patients with definite diagnosis by the Schumacher criteria (n = 61) we found significant correlations between CSF immunoglobulin content (absolute gamma-globulin value [aggv]) and quantified MRI factors (r = .47), between aggv and the sum of VEP latencies of both eyes (r = .53), and also between MRI and VEP changes (r = .62). This was not true for the patients with a probable MS diagnosis and for patients with first attacks. No correlations were evident between aggv and disability status or duration of the illness. The results give support to recent neuropathologic and experimental findings in animals indicating close pathogenic connections between CSF immunoglobulins and demyelination in MS.

Pursuit and optokinetic deficits following chemical lesions of cortical areas MT and MST.

1. Previous experiments have shown that punctate chemical lesions within the middle temporal area (MT) of the superior temporal sulcus (STS) produce deficits in the initiation and maintenance of pursuit eye movements (10, 34). The present experiments were designed to test the effect of such chemical lesions in an area within the STS to which MT projects, the medial superior temporal area (MST). 2. We injected ibotenic acid into localized regions of MST, and we observed two deficits in pursuit eye movements, a retinotopic deficit and a directional deficit. 3. The retinotopic deficit in pursuit initiation was characterized by the monkey's inability to match eye speed to target speed or to adjust the amplitude of the saccade made to acquire the target to compensate for target motion. This deficit was related to the initiation of pursuit to targets moving in any direction in the visual field contralateral to the side of the brain with the lesion. This deficit was similar to the deficit we found following damage to extrafoveal MT except that the affected area of the visual field frequently extended throughout the entire contralateral visual field tested. 4. The directional deficit in pursuit maintenance was characterized by a failure to match eye speed to target speed once the fovea had been brought near the moving target. This deficit occurred only when the target was moving toward the side of the lesion, regardless of whether the target began to move in the ipsilateral or contralateral visual field. There was no deficit in the amplitude of saccades made to acquire the target, or in the amplitude of the catch-up saccades made to compensate for the slowed pursuit. The directional deficit is similar to the one we described previously following chemical lesions of the foveal representation in the STS. 5. Retinotopic deficits resulted from any of our injections in MST. Directional deficits resulted from lesions limited to subregions within MST, particularly lesions that invaded the floor of the STS and the posterior bank of the STS just lateral to MT. Extensive damage to the densely myelinated area of the anterior bank or to the posterior parietal area on the dorsal lip of the anterior bank produced minimal directional deficits. 6. We conclude that damage to visual motion processing in MST underlies the retinotopic pursuit deficit just as it does in MT. MST appears to be a sequential step in visual motion processing that occurs before all of the visual motion information is transmitted to the brainstem areas related to pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)

Directional pursuit deficits following lesions of the foveal representation within the superior temporal sulcus of the macaque monkey.

Ibotenic acid lesions of the middle temporal visual area (MT) have previously been shown to impair a monkey's ability to initiate smooth pursuit eye movements to targets moving in the extrafoveal visual field (30). This is a retinotopic deficit: pursuit is impaired in all directions within the affected portion of the contralateral visual field. In the present experiments we analyzed the effects of lesions of the foveal representation of MT on the maintenance of foveal pursuit. Injections of ibotenic acid were directed toward the representation of the fovea within MT but spread into extrafoveal regions of MT and adjacent visual areas within the superior temporal sulcus. Chemical lesions of the foveal representation produced a directional deficit in the maintenance of pursuit: the monkey failed to match eye speed to target speed when pursuing a target that moved toward the side of the brain with the lesion. This deficit was evident regardless of the part of the visual field in which target motion began, and pursuit at higher target speeds was more severely affected. The directional deficit was qualitatively similar to pursuit deficits observed in human patients following large parietal-occipital lesions. Extension of the lesions into extrafoveal regions of the contralateral visual field representation also resulted in retinotopic deficits for pursuit initiation: the monkey was unable to match the speed of its pursuit eye movement to that of a target or to adjust the amplitude of its saccade to compensate for target motion. The errors in pursuit speed and saccade amplitude for initiation of pursuit into the contralateral visual field were linearly related, which supports the hypothesis that both deficits arise from damage to the same underlying visual motion processing mechanism. The selectivity of the retinotopic deficit for motion information was also investigated by reducing retinal motion through the use of a stabilized image. After the lesion, the monkeys continued normal pursuit when a position error was present during stabilization, supporting the view that the deficit was related to loss of motion but not position information.

Deficits in visual motion processing following ibotenic acid lesions of the middle temporal visual area of the macaque monkey.

Physiological experiments have produced evidence that the middle temporal visual area (MT) of the monkey is selectively involved in the analysis of visual motion. We tested this hypothesis by studying the effects of small chemical lesions of MT on eye movements made in response to moving as opposed to stationary visual targets. We observed two deficits for eye movements made to moving targets: a monkey's ability to match the speed of his smooth pursuit eye movements to the speed of the moving target was impaired, and a monkey's ability to adjust the amplitude of a saccadic eye movement to compensate for target motion was impaired. In contrast, saccades to stationary targets were unaffected by the MT lesions, suggesting that monkeys with MT lesions had more difficulty responding to moving than to stationary stimuli. These results provide the first behavioral evidence that neural processing in MT contributes to the cortical analysis of visual motion.

Punctate chemical lesions of striate cortex in the macaque monkey: effect on visually guided saccades.

Chemical agents which reversibly or irreversibly disrupt neural processing offer several advantages over traditional techniques for behavioral studies of the central nervous system. In order to evaluate the utility of chemical agents for a behavioral analysis of visual cortical function in primates, we have tested the effects of muscimol and ibotenic acid on the function of striate cortex in awake, behaving monkeys. We studied the monkey's ability to generate saccadic eye movements to visual targets at various locations in the visual field following an injection of one or the other chemical solution into a topographically identified location in striate cortex. Our results show that deficits in the generation of visually guided saccades following such injections are similar to those that result from surgical ablation of striate cortex, although recovery is more rapid following the injections. The experiments indicate that, with certain restrictions, chemical inactivation is a useful technique for behavioral analysis of visual cortical function.

Plasticity in the binocular correspondence of striate cortical receptive fields in kittens.

The influence of visual experience on the correspondence in position and orientation of receptive fields in the two eyes of cortical neurones was studied. Kittens were reared viewing the environment through lenses that magnified the image by 9% in one direction (meridional size lenses) with axes of magnification oriented 45 degrees left and right of vertical for the two eyes. The unequal deformations in the two eyes produced gradients of position disparity and systematic variation of orientation disparity which could not be influenced by eye movements. Two types of arrangement of the lenses, producing opposite disparities, were used; each was worn by two kittens. The receptive fields of cortical neurones were studied in the four kittens aged 3-4 months. In the binocular cells, the positions of the response fields were plotted, and the preferred orientations determined, using automatic stimulus variation, quantitative analysis, and eye-drift correction. By means of regression analysis, the degree of 'interocular deformation' was assessed; a coefficient D was derived from the positions, an angle beta from the orientations. D specified the position incongruity as a fraction of retinal eccentricity, beta the difference between the orientation incongruities of cells with near-vertical and near-horizontal receptive fields. Both D and beta were found to be of opposite signs in the two groups of kittens, as predicted by the optical effects of the lenses. The difference in D between the groups was 0.197 (predicted: 0.172); the difference in beta was 17.0 degrees (predicted: 18.9 degrees). Thus, the difference in visual environment had been completely compensated by adjustments in the positions as well as the orientations of the receptive fields. Since D and beta are independent of the alignment of the eyes, the differences between the groups reflected different functional connexions at the cortical level. Possible advantages of plasticity for the development of binocular vision are discussed. It is argued that the plasticity demonstrated here reflects a more general property of cortical receptive fields.

Projections to the visual cortex in the golden hamster.

Retrograde transport of horseradish peroxidase (HRP) was used to determine the origins of afferent connexions to the visual cortex (areas 17, 18a and 18b) in the hamster. The distribution of neurons projecting to the visual cortex from other cortical areas, from the thalamus and from the brainstem was studied using a computer technique for three-dimensional reconstruction. There is a topographically organized projection from the dorsal lateral geniculate nucleus to area 17, but probably to no other of the areas studied. The lateral posterior nucleus of the thalamus (LP) projects to area 18a and weakly to area 17. The lateral nucleus (L) projects to area 18b and also, probably, weakly to area 17. The cortical projections from LP and L are also organized topographically but relatively grossly compared with the geniculo-cortical pathway. There are reciprocal association projections between area 17 and areas 18a and 18b. Areas 18a projects weakly to 18b. The main commissural connexions of the posterior neocortex are between the area 17/18a boundary zones in the two hemispheres, with little between the bodies of area 17. Labelled neurons were found bilaterally in the locus coeruleus, more ipsilaterally than contralaterally, after multiple injections into the visual cortex: single, small injections sometimes resulted in the labelling of a single cell body in the locus coeruleus.

Uptake of horseradish peroxidase by geniculo-cortical axons in the golden hamster: analysis by computer reconstruction.

Micro-injections of horseradish peroxidase (HRP) were made into the visual cortex of the golden hamster. The "projection lines" of labelled neurons in the dorsal lateral geniculate nucleus (LGNd) were three-dimensionally reconstructed, using a computer graphics technique. The lines run rostrally and medially from their origins at the lateral surface of the nucleus. Using an anatomically determined retinotopic map of the LGNd, the positions of all labelled cells near the lateral surface were converted into equivalent visual field co-ordinates and displayed on a physiologically determined retinotopic map of the primary visual cortex. Comparison between the scatter of these equivalent retinotopic loci and an actual reconstruction of the injection site revealed that: 1. there was general agreement between the independent retinotopic maps of LGNd and visual cortex; 2. there was greater retinotopic scatter of labelled LGNd cells than could be accounted for by the area of tissue injury in the cortex; 3. the retinotopic scatter matched more closely the total visible halo of HRP staining in the grey matter; 4. HRP can be taken up from a cytoarchitectonic field into which it diffuses after injection into a neighbouring area; 5. HRP is probably not taken up by undamaged axons in the white matter. These results are compared with those obtained in other animals and other systems. No general rules emerge, but the possibility of uptake from wide areas of diffusion must be considered when interpreting results of HRP injection.

Reversal of the morphological effects of monocular deprivation in the kittens's lateral geniculate nucleus.

1. Eleven kittens were deprived of vision in one eye until the age of between 5 and 14 weeks. Their eyes were then reverse-sutured, they were allowed to survive for a further 3-63 days, and their brains were then examined histologically. 2. Measurement of the cross-sectional area of cells in the lateral geniculate nucleus (LGN) showed that when the reversal of lid suture was performed at the age of 8 or 14 weeks, the mean cell size was smaller in laminae connected to the initially closed right eye than it was in other laminae. 3. When the reversal of lid suture took place at 5 or 6 weeks of age there was a reversal of interlaminar size differences: the initially deprived eye was then connected to laminae containing larger cells. Even within 3 days after the reversal of lid suture, most of the morphological effects of the initial suture had been abolished, and they were fully reversed within 12 days. 4. These results are compared with physiological changes in the visual cortex of these and similarly reared animals.

[Migraine and the vestibular apparatus (author's transl)]. / Migräne und Vestibularapparat

Thirty patients with simple or ophthalmic migraine had an otoneurological examination. 13% complained of vertigo during attacks of migraine, 17% of giddiness and 6.7% of tinnitus. The usual tests for equilibrium were normal. On electronystagmographical examination 17% of the patients showed only pathological spontaneous nystagmus, 33% only disturbances of caloric response and 7% a combination of both. Audiological testing was normal. The incidence of vestibular disturbances, particularly sensitivity differences of the labyrinths, was significantly greater in the group of patients with migraine than in a control group of 30 healthy persons (P less than or equal to 0.025). On the average, the sensitivity differences, in terms of duration of reactive nystagmus, were greater for these than for the healthy persons (P less than or equal to 0.01). Patients with vestibular disturbances did not show a greater frequency of pathological EEG readings than patients with normal vestibular function. Some hypotheses concerning the pathogenesis of vestibular symptoms as found in migrainous patients are mentioned.